1. Field of the Invention
The present invention relates to hydraulic systems, and more particularly to hydraulic tools which require a means for cooling the hydraulic fluid.
2. History of the Prior Art
Tools such as chain saws, railroad tie pullers, jackhammers and the like are capable of being powered by a number of different sources including gasoline engines, electric motors, pneumatic systems and hydraulic systems. For most power tools, and particularly for those requiring substantial amounts of power, hydraulic operation is potentially advantageous for a number of reasons including the fact that large amounts of power can be provided the tool from a hydraulic system of given size. In a pneumatic system a like amount of power typically requires equipment of considerably larger size. Such factors become important not only in terms of the cost of the power equipment required, but particularly in terms of the size and weight of the equipment required to be transported by truck or other means to various job sites.
While hydraulic systems have proven to be efficient and effective power sources in many respects, they also have cooling problems which may make them unsuitable or undesirable for certain applications such as those in which the ambient temperature is relatively high. As the hydraulic fluid is pumped under substantial pressure to the tool, used in the tool and then returned to a reservoir for storage prior to recirculation, it becomes heated. The heated fluid becomes uncomfortable and poses a potential danger to workmen and other personnel, particularly if the temperature becomes too high and one or more portions of the system become prone to leaking or bursting. Moreover, as the hydraulic fluid is heated to higher temperatures, the viscosity thereof changes such that is poses even greater leakage problems.
Various techniques are commonly employed to cool hydraulic fluid including an arrangement in which the hot fluid is fed into a radiator-type structure having plural fins in contact with a coil through which the heated fluid flows. A multiplicity of small elements in the flow path of the hydraulic fluid attempt to create a turbulence so as to enhance transfer of heat from the hydraulic fluid to the air surrounding the radiator-like structure. While such cooling techniques are adequate for certain applications including most applications where ambient temperature is relatively low, they have proven to be inadequate for various applications and particularly those where ambient temperature is relatively high. For example, such cooling arrangements are typically capable of reducing the temperature of the hot hydraulic fluid to within 40.degree.-50.degree. F. of ambient temperature and no more. If the temperature on a street corner where a jackhammer or other tool is being used is 90.degree.-100.degree. F. on a summer day, it may be impossible to cool the hydraulic fluid below about 140.degree.-150.degree. F. Experiments have shown that temperatures in excess of about 114.degree. F. produce discomfort among workers. Such temperature levels, aside from making workmen uncomfortable because of the heat given off by the equipment, may not only be dangerous but may violate various health and safety standards.
Accordingly, it would be desirable to be able to provide a hydraulic system in which heated hydraulic fluid is efficiently and effectively cooled to safe and comfortable levels despite the presence of relatively high ambient temperatures.